I have faced some huge servers before, 120's and 130's. That one didn't look too big. I've seen bigger. I would guess maybe 110-115. The thing is you can hit as hard as you want, but if the ball is just coming right to the person then it's kinda useless. All that is required is to block it back. If I had the choice between a person that can hit 125 mph serves vs. a person that can hit 105-100 mph with good placement. Give me a person that can use the angles and placement over a big server any day of the week.
I believe in Taylor Dent.